Rubber for a tire rim cushion or rubber finishing sustains a strong compressive load in order to support the load of a vehicle, so there is a demand for the rubber hardness to be high. In addition, there is also a demand for the rubber to have properties such as resistance to permanent deformation (setting resistance) and wear resistance, even when undergoing compressive deformation.
On the other hand, increases in environmental awareness in recent years have led to a demand for improvements in fuel efficiency of tires. One means for reducing the heat build-up of rubber for a tire rim cushion or rubber finishing is a method of reducing the compounding ratio of fillers, but such a means causes a decrease in hardness and also diminishes the wear resistance.
Therefore, it has been very difficult to achieve at a high degree both low heat build-up as well as hardness, wear resistance, and setting resistance with conventional technology.
In Japanese Unexamined Patent Application Publication No. 2006-56978A, a rubber composition for a tire rim strip containing polybutadiene rubber having a specific viscosity ratio is disclosed. However, in the technology described in Japanese Unexamined Patent Application Publication No. 2006-56978A, it is not possible to satisfy both low heat build-up as well as hardness, wear resistance, and setting resistance at a high level.